1. Field of the Invention
The present invention relates to a speed control system for a bicycle for controlling a change speed device through a change speed wire, having:
a control member movable between a first shift end and a second shift end;
a device connected to one end of the change speed wire, and movable in a wire winding direction and in a wire unwinding direction, the take-up device being urged in the wire unwinding direction;
a one-way transmission device for transmitting only movement toward the second shift end of the control member to the takeup device, the takeup device being movable in the wire winding direction by the movement toward the second shift end;
a position retaining device for retaining the take-up device in a plurality of winding positions; and
a retention canceling device for canceling retention of the take-up device by the position retaining device, and allowing the take-up device to move in the wire unwinding direction.
2. Description of the Related Art
Conventional bicycle speed control systems of the type noted above are known from Japanese Patent Publication Kokai No. 1990-88384 and U.S. Pat. No. 5,012,692, for example. These control systems include a release lever besides a shift lever, for releasing a change speed wire take-up reel from a position retaining device. Further, a spring is provided for urging the take-up reel in a wire unwinding direction in order to expedite rotation in the unwinding direction of the take-up reel after its release from the position retaining device.
In such a construction, the shift lever returns to home position after each shifting operation. This feature provides the advantage of allowing the shift lever to be operated within an optimal stroke range from the human engineering point of view, even when the shift lever is operated to provide a speed many stages away from the home position. That is, the shift lever is shifted back and forth plural times to effect change speed in the wire winding direction, i.e. in a positive direction. Conversely, when effecting change speed in the wire unwinding direction, i.e. in a negative direction, the release lever is operated to release the take-up reel from the position retaining device, whereby the take-up reel automatically rotates backward.
However, since the release lever is provided besides the shift lever, the cyclist could easily operate the wrong lever in a change speed operation. As a result, there is not a little chance of effecting change speed in the wrong direction. Furthermore, this type of speed control system may be disposed adjacent a grip of a handlebar. In such a case, the position of the shift lever optimal from the human engineering point of view is limited for manipulation with the thumb and finger. Consequently, where the two levers are provided, at least one must be located in a position difficult to operate.
In addition, according to the above construction, the force of the spring for urging the take-up reel in the wire unwinding direction presents a resistance to turning of the shift lever in the wire winding direction. This provides the drawback of giving a heavy feeling when the cyclist operates the shift lever in the wire winding direction.